The present invention relates to an apparatus and method for controlling a vehicle air conditioner having a variable displacement compressor.
In the prior art, when an engine of a vehicle is idling, the activation of a variable displacement compressor, which is incorporated in an air conditioner of the vehicle, results in the execution of idle-up control, which increases the idle speed of the engine. The increase in the idle speed produces the torque required to drive the compressor and prevents the engine from stalling. Further, the increase in the idle speed enables the compressor to cope with high cooling loads.
There is a recent trend for decreasing the idle speed to improve fuel efficiency. However, the execution of the idle-up control when the compressor is activated decreases fuel efficiency.
The prior art idle-up control is always executed when the engine is idling and the compressor is activated. Accordingly, the idle speed fluctuates whenever the compressor is activated or deactivated. This increases the vibrations and noise of the vehicle.
Further, the increased amount of the idle speed during the idle-up control is determined presuming that the torque required to drive the compressor is maximal, that is, the displacement of the compressor is maximal. Accordingly, if, for example, the displacement of the compressor is small and the torque required to drive the compressor is low, the idle speed is increased in an unnecessary manner. This is not desirable from the viewpoint of fuel efficiency.
It is an object of the present invention to provide an apparatus and method for controlling the displacement of a variable displacement compressor in accordance with the engine idle speed.
To achieve the above object, the present invention provides a vehicle air conditioner including a refrigerant circuit that incorporates a variable displacement compressor driven by an engine of the vehicle. The air conditioner includes a control valve for varying the displacement of the compressor. An air conditioner control unit controls the control valve. The control valve includes a pressure sensing mechanism having a valve body and a pressure sensing member connected to the valve body and moved in accordance with a pressure difference between two pressure monitoring points located along the refrigerant circuit. The pressure difference corresponds to the displacement of the compressor and alters the moved amount of the pressure sensing member. A pressure difference adjusting actuator is controlled by the air conditioner control unit. The pressure difference adjusting actuator applies a force, which counters the movement of the pressure sensing member, to the valve body to move the valve body and alter the moved amount of the pressure sensing member. The pressure difference adjusting actuator further adjusting the force applied to the valve body to alter the moved amount of the pressure sensing member and vary the displacement of the compressor. The air conditioner control unit changes the force of the pressure difference adjusting actuator applied to the valve body to adjust the pressure difference and vary the displacement of the compressor. The changes in force when the engine is running at an idle speed is more gradual than when the engine is running at a speed other than the idle speed.
A further perspective of the present invention is a method for controlling a vehicle air conditioner including a refrigerant circuit that incorporates a variable displacement compressor driven by an engine of the vehicle, a pressure sensing mechanism, and a pressure difference adjusting actuator. The pressure sensing mechanism has a valve body and a pressure sensing member, which is connected to the valve body and moved in accordance with the pressure difference between two pressure monitoring points located along the refrigerant circuit. The pressure difference adjusting actuator applies a force, which counters the movement of the pressure sensing member, to the valve body to move the valve body, and changes the force applied to the valve body to alter the moved amount of the pressure sensing member, adjust the pressure difference, and vary the displacement. The method includes changing the force of the pressure difference adjusting actuator applied to the valve body to adjust the pressure difference and vary the displacement of the compressor when the engine is running at an idle speed. The changes in force when the engine is running at the idle speed are more gradual than when the engine is running at a speed other than the idle speed.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.